Sex education should become part of the national curriculum, with special training for teachers in how to deliver it, the British Medical Association urges in its latest report.
The BMA also calls for the repeal of the controversial Section 28 law, which bans local authorities from "promoting" homosexuality, saying it has proved "positively harmful" to sex education in schools.
The law does not relate to schools, but the BMA says that many teachers have been left confused by it and that it has inhibited their teaching.
Calling for a public debate, the report, School Sex Education: good practice and policy, says sex education has been proven to work.
Young people start sexual relations later, the report says, and are more likely to use condoms and other forms of contraception, leading to a fall in teenage pregnancies.
But sex education will never be given the attention - or the resources - it deserves until it becomes part of the national curriculum.
"Good teaching focuses on sexual feelings, values, communication and relationships," the report says. Sex education should, therefore, become part of a total programme of personal social and health education - "life preparation".
The recommendation chimes with growing calls for pupils to be better prepared for adulthood, with courses in life skills such as parenting and civics, allowing them to play their full part in a democracy.
The BMA is calling for sex education to become a compulsory module within initial teacher training, with more resources directed to in-service training and to monitoring standards of sex education teaching.
The report brings together evidence from doctors and various investigations into the success of sex education programmes, and offers advice to teachers on good practice. It recommends that schools involve doctors and other health professionals more but says that teachers should continue to play the lead role.
And it stresses the importance of consulting parents on sex education, saying many parents want guidance on how to talk about sexual matters with their children. The school should complement parents, not override them.
Teachers also need to consider the views of young people and the diversity of their attitudes, maturity, values, home environment, and religious, cultural or ethnic backgrounds.
The BMA also recommends that teachers use case studies when talking about sex with children, to allow them to discuss realistic scenarios without disclosing their own experiences in the classroom.
Pupils should be able to turn to someone for confidential help and advice.And they need responsible teaching about homosexuality.
For those growing up gay, lesbian or bisexual, it is important to address the risks to mental or physical health from bullying, isolation, or low self-esteem. Others need to be educated about the effects of stereotyping and prejudice.
Section 28 of the Local Government Act 1988, however, has undermined the ability of schools to give neutral advice and support to young people by sowing confusion and concern, the BMA says.
Legally, sex education is the responsibility of the school governors, not the local authority. The Section, therefore, has no bearing on schools at all. But it is often wrongfully advanced as a reason for not teaching about homosexuality. That inhibits some teachers and gives others an excuse to ignore the subject.
"The Section has, therefore, proved positively harmful in ensuring issues of sexuality are responsibly addressed within schools," the report says. "It should be repealed."
School Sex Education: good practice and policy (BMA Board of Science and Education, April 1997) is available from 0171 383 6755.